Microseismic monitoring and borehole geophysics relies on detecting very small “events” from remote sources with receivers located in a borehole. To attain accuracy, however, it is necessary that the signals be sufficiently greater in amplitude than noise levels. This limits the ability to detect small and/or far remote events which attenuate during travel through rock and other formations.
Stacking of geophones or other sensors within a receiver is a common procedure for improving the signal-to-noise ratio (SNR) of a recorded seismic event. However, while the stacking of many sensors in a single tool may be useful in summing signals so that overall levels are large enough for accurate digitization, such stacking of sensors does little for noise cancellation because all sensors detect the same cultural noise. In addition, all of the data collected by sensors in the same receiver will reflect the same electronic noise when amplified and digitized. When stacking receivers, the only noise that might cancel when two events are summed together is noise that is self-generated within the sensor. However, self-generated noise within the sensor is usually very small.